libceph: fix race between delayed_work() and ceph_monc_stop()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: libceph: fix race between delayed_work() and ceph_monc_stop() The way the delayed work is handled in ceph_monc_stop() is prone to races with mon_fault() and possibly also finish_hunting(). Both of these can requeue the delayed work which wouldn't be canceled by any of the following code in case that happens after cancel_delayed_work_sync() runs -- __close_session() doesn't mess with the delayed work in order to avoid interfering with the hunting interval logic. This part was missed in commit b5d91704f53e ("libceph: behave in mon_fault() if cur_mon < 0") and use-after-free can still ensue on monc and objects that hang off of it, with monc->auth and monc->monmap being particularly susceptible to quickly being reused. To fix this: - clear monc->cur_mon and monc->hunting as part of closing the session in ceph_monc_stop() - bail from delayed_work() if monc->cur_mon is cleared, similar to how it's done in mon_fault() and finish_hunting() (based on monc->hunting) - call cancel_delayed_work_sync() after the session is closed

References

• https://git.kernel.org/stable/c/1177afeca833174ba83504688eec898c6214f4bf
• https://git.kernel.org/stable/c/63e5d035e3a7ab7412a008f202633c5e6a0a28ea
• https://git.kernel.org/stable/c/34b76d1922e41da1fa73d43b764cddd82ac9733c
• https://git.kernel.org/stable/c/20cf67dcb7db842f941eff1af6ee5e9dc41796d7
• https://git.kernel.org/stable/c/2d33654d40a05afd91ab24c9a73ab512a0670a9a
• https://git.kernel.org/stable/c/9525af1f58f67df387768770fcf6d6a8f23aee3d
• https://git.kernel.org/stable/c/33d38c5da17f8db2d80e811b7829d2822c10625e
• https://git.kernel.org/stable/c/69c7b2fe4c9cc1d3b1186d1c5606627ecf0de883